Ag thin films of pure Ag or Ag alloy and like have superior optical characteristics such as high reflectivity and transmissivity and a low extinction coefficient, superior thermal characteristics with high thermal conductivity, and superior electrical characteristics with low electrical resistance, as well as superior surface smoothness. Therefore, the Ag thin films have been broadly applied to many applications including: reflective films, semi-transparent reflective films, and thermal diffusion films for information recording media; low-E films for heat ray reflective/shield films; and shield films for electromagnetic wave shield films.
Such kinds of Ag thin films are produced, for example, by sputtering using an Ag sputtering target. Many attempt for improving the Ag sputtering target has been conducted (for example, Japanese Patent Application Laid-open Publication No. 9-324264 and Japanese Patent Application Laid-open Publication No. 2000-239835). Specifically, Japanese Patent Application Laid-open Publication No. 9-324264 reports that the sputtering target formed by a silver alloy (or silver based composite metal) comprising 0.1 to 2.5 at % gold and 0.3 to 3 at % copper can prevent adverse effects caused by ambient gas during sputtering such as oxygen (reduction of optical transmissivity and optical reflectivity on the short wavelength side of the visible region). Further, Japanese Patent Application Laid-Open Publication No. 2000-239835 discloses that setting the ((111)+(200))/(220) plane orientation ratio of the Ag sputtering target equal to or more than 2.20 can raise sputtering rates, resulting in improved thin film production efficiency.